Synthesis of thiol-derivatized europium porphyrinic triple-decker sandwichcomplexes for multibit molecular information storage

The storage of multiple bits of information at the molecular level requires molecules with a large number of distinct oxidation states. Lanthanide tri ple-decker sandwich molecules employing porphyrins and phthalocyanines affo rd four cationic states and are very attractive for molecular information s torage applications. Five triple-decker building blocks have been prepared of the type (phthalocyanine)Eu(phthalocyanine)Eu(porphyrin), each bearing o ne iodo, one ethyne, or one iodo and one ethyne group attached to the porph yrin unit. Two triple-decker building blocks with different oxidation poten tials were derivatized with an S-acetylthiophenyl unit for attachment to an electroactive surface; To explore the preparation of arrays comprised of t riple deckers, which may lead to the storage of a larger number of bits, tw o types of dyads of triple deckers were prepared. An ethyne-linked dyad of triple deckers bearing one S-acetylthiophenyl unit was prepared via repetit ive Sonogashira couplings, and a butadiyne-linked dyad was prepared via a m odified Glaser coupling. The triple deckers were characterized by absorptio n spectroscopy, laser-desorption mass spectrometry, and H-1 NMR spectroscop y. The thiol-derivatized triple deckers form self-assembled monolayers (SAM s) on gold via in situ cleavage of the thiol protecting group. The SAM of e ach array-is electrochemically robust and exhibits three well-resolved, rev ersible oxidation waves. These electrochemical characteristics indicate tha t these types of molecules are well suited for storing multiple bits of inf ormation.